Generally, full-wave rectifying circuits are used as converters to obtain a DC voltage from a single-phase AC voltage input from a single-phase AC power source. However, the output of the full-wave rectifying circuits contains power ripple having a frequency twice that of the single-phase AC voltage. Thus, reduction in this power ripple requires a power buffer circuit that buffers the power between an output of the full-wave rectifying circuit and a load.
Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, The 2010 Annual Meeting of the Institute of Electrical Engineers of Japan, 4-057 (2010), Ohnuma, Itoh, “Experimental Verification of Single Phase to Three Phase Converter Using an Active Buffer circuit with a Charge Circuit”, 2010 IEE—Japan Industry Applications Society Conference, 1-124 (2010), Ohnuma, Itoh, “Basic Investigation and Capacitance Reduction method of A Novel Single-Phase to Three-Phase Power Converter”, The papers of Technical Meeting on Semiconductor Power Converter, IEE Japan, SPC-08-16 (2008), Japanese Patent Application Laid-Open No. 2011-193678, Japanese Patent Application Laid-Open No. 2014-107935, Japanese Patent No. 5454732 and Japanese Patent Application Laid-Open No. 2014-96976 disclose a technique for connecting a capacitor to a DC link through a switching element. In the proposed technique, the capacitor (hereinafter also referred to as a “buffer capacitor”), which functions as a voltage source, drives a load together with a power supply voltage to compensate for the power ripple as well as reduce the electrostatic capacity required for the buffer capacitor.
Particularly, Ohnuma, Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, The 2010 Annual Meeting of the Institute of Electrical Engineers of Japan, 4-057 (2010), Ohnuma, Itoh, “Experimental Verification of Single Phase to Three Phase Converter Using an Active Buffer circuit with a Charge Circuit”, 2010 IEE—Japan Industry Applications Society Conference, 1-124 (2010), Japanese Patent Application Laid-Open No. 2011-193678, Japanese Patent Application Laid-Open No. 2014-107935, Japanese Patent No. 5454732 and Japanese Patent Application Laid-Open No. 2014-96976 also propose a technique that achieves a function of a boost chopper using a reactor and a switch to boost a voltage across a buffer capacitor (hereinafter referred to as a “both-end voltage”).
Ohnuma, Itoh, “Experimental Verification of Single Phase to Three Phase Converter Using an Active Buffer circuit with a Charge Circuit”, 2010 IEE—Japan Industry Applications Society Conference, 1-124 (2010) teaches a case (a discontinuous mode) where a reactor current flowing through a reactor is discontinuous to achieve the function of the boost chopper. A command value of the reactor current (hereinafter also referred to as a “reactor current command”) depends on a current to be input to a full-wave rectifying circuit. Ohnuma, Itoh, “Experimental Verification of Single Phase to Three Phase Converter Using an Active Buffer circuit with a Charge Circuit”, 2010 IEE—Japan Industry Applications Society Conference, 1-124 (2010) also teaches a technique for estimating the input current by obtaining the maximum value and the minimum value of a both-end voltage.
Furthermore, Japanese Patent Application Laid-Open No. 2014-107935 discloses a technique for maintaining an average of a both-end voltage. Japanese Patent No. 5454732 teaches cases where the reactor current flows not only in the discontinuous mode but also in a critical mode.